With the development of the integrated circuit technology, the Charge Pump Phase-locked Loop is widely used in the wireless telecommunication, the frequency synthesizer and the clock recovery Circuit because its features of the low power consumption, the high speed, the low jitter and the low cost, etc.
CMOS (Complementary Metal Oxide Semiconductor) image sensor is a kind of amplifying device for voltage controlling. It is the basic component of CMOS digital integrated circuit. It is mainly used in the semiconductor device transforming the optical image into electrical signals. Usually, the CMOS image sensor need to use the technology of charge pump in order to generate a voltage higher than the source voltage on silicon wafer. The generated high voltage is generally used for driving the pixel units of the CMOS image sensor, for example the reset end and shift end in the pixel unit.
FIG. 1 is the CMOS charge pump circuit layout of the prior art. As shown in FIG. 1, when the UP signal switches, the output voltage Vout will be pulled to the Earth End GND through the switches M1 and M2. A relatively big voltage jump is generated. Likewise, when the DN signal switches, the output voltage Vout will be pulled to the source voltage VDD through the switches M3 and M4. And a relatively big voltage jump is generated, which affect the stability of the circuit.
Chinese Patent (CN101478644A) discloses a charge pump control circuit and method of the CMOS image sensor. The said charge pump control circuit of the CMOS image sensor compromises: the high voltage limit comparing unit used for comparing the output voltage of the charge pump to the high voltage limit; the horizontal synchronizing signal providing unit used for providing synchronizing signal based on horizontal readout time. The horizontal synchronizing signal reaches the high level earlier than the horizontal selection signal. And the horizontal synchronizing signal changes into low level on the rising edge. A charge pump control unit is further included. The charge pump is switched on when the horizontal synchronizing signal is high level and output voltage of the charge pump is lower than the high voltage limit. The chare pump is switched off when the output voltage of the charge pump is higher than the high voltage limit. The CMOS image sensor charge pump control circuit and method thereof can avoid reading out noise.
The invention raises the output voltage of the charge pump to the high voltage limit. The output voltage of the each line of the pixel unit of the CMOS image sensor in the stage of horizontal readout is same. It avoided the noise due the different output voltage of each line of the pixel unit of the CMOS image sensor in the stage of horizontal readout. However, the invention did not solve the problem of voltage jump due to the logic signal switching in the CMOS charge pump circuit.
Chinese Patent (CN 103259536A) discloses a charge pump circuit based on the standard CMOS process, which is applied to the low current mismatch and the low current change in the charge pump phase-locked loop circuit. The charge pump circuit consists of the current bias circuit, the reference current circuit, the output current circuit and the amplifier.
In this invention, the negative feedback loop is formed by the amplifier. The negative feedback loop is used to reduce the mismatch between the charge current caused by change of voltage of the output and the discharge current. The current with a positive output voltage coefficient is added with the current with a negative output voltage coefficient in order to reduce the overall changes of the charge current and the discharge current during the voltage change in the output end. However, this patent did not solve the problem of the big voltage jump when the signal switches. And the stability of the circuit is affected.